Sleep disturbances are among the most common mental health problems for the 65 + age group and is undoubtedly an important agent in the transition from "successful" to "usual" or even "pathological" aging. Thus, there is a need to better understand the psychobiological sleep correlates of successful aging as well as those associated with the changes of more usual aging, during which physiological and psychological functioning show impairment, but do not yet qualify as diseased. We aim to test a model which posits that increasing medical burden and negative life events in those who have aged successfully will eventually impair biological regulatory processes which maintain the internal milieu, i.e., homeostatic processes which we now know include sleep. Within this context, we currently have 76 "successfully" aged men and women (of the total N = 100) enrolled in a three year longitudinal design with annual sleep and semiannual clinical assessments to test the following hypotheses. l) With advancing age, the increasing burden of medical illness and negative life events will have a destabilizing effect on mood, producing a negative shift in affect balance, as "successful" aging gives way to "usual" aging. Negative shift in affect balance, associated with depressive symptoms, will mediate much (though not all) of the impact of medical burden and negative life events on sleep efficiency, sleepiness index, and sleep quality. In addition, increasing medical burden will have a direct (and deleterious) effect on measures of sleep disordered breathing, with increasing medical burden leading to increased frequency and severity of sleep disordered breathing. 2) Social support and stability of social rhythms will be important moderators (buffers), helping to protect elderly from the onset of depressive symptoms and hence to protect sleep. 3) Sleep itself will have a major influence upon subsequent levels of adaptation in both physical and psychological dimensions.